When grinding flaxseeds in a coffee grinder, is it safe to add some water inside?

Coffee grinders are designed for dry grinding, not wet grinding. The mention of water in your quote is for a blender, not a grinder. There are also wet-dry grinders, but that's not one.

So, I'm not sure if it's actually dangerous, but it's certainly not designed to have water in it. And either way, since it's not meant for wet grinding, it's not likely to grind wet things well.

Blenders, on the other hand, are designed for liquids, so it makes sense that blending a slurry might work better than something dry.

I can't speak for yours directly but coffee grinders are usually sealed. The dust generated by grinding is bad for motors, and they have to be washed without large amounts of water being held in the mechanism to run down into the motor.

I have a small grinder of this type, like yours marketed for coffee and other things. Mine is in the form of a food processor attachment. It is properly sealed. You could use it as a blender so long as you put it together in the right order. The manual ought to be clear if you can't use liquids as they're marketing it as a spice grinder, and it wouldn't be unreasonable to grind sources with oil for a marinade (for example).

Having looked at the pictures in a bit more detail it seems like you shouldn't use a lot of liquid as there doesn't seem to be much of a seal where the top attaches.

The article you quoted from only says

adding a bit of water or liquid to the seeds will make the blending process much easier

It doesn't say that you have to add water. I have the same grinder as you and mainly use it for grinding spices (it's not really suitable as a coffee grinder unless you like bad tasting coffee).

So, grind the seeds dry and use how intended (either by adding water or adding the ground seeds to something else).

I ground peppermints in my grinder (the same type as shown above) and it did well but left peppermint stuck to the bottom. It was difficult to get out with a damp cloth, so the only way was to either melt the peppermint out with hot water or chip it out with a knife and I did not want to scratch up the inside. I was wondering if water was safe to put in the grinder, which is how I came across this. I wanted to pour hot water out of my electric kettle with a little dish soap and then turn it on to spin around inside until the peppermint was gone.

I poured the water and dish soap inside, and luckily all I had to do was swish it around a little a few times and the grinder was cleaned perfectly. I did not turn the grinder on at all, and it was unplugged the entire process.

The part I wanted to mention was that around the edge, I am seeing where water seeped inside a little. I have no clue if it got to the motor at all, but I am leaving the grinder upside down to dry out before I use it again in case. The edge around the silver pan that holds the blades is where the water seeped in. I also noticed that when I poured water in, some bubbles came up from around the blades which tells me water was able to get through around them as well.

While I cannot 100% say that I know how safe this is or what will happen (because I cannot see where exactly the water seeped into) I would not recommend putting liquid into one of these and starting it as it can easily seep through. I realize the question at hand was about a few drops of water into dry substance which is a bit different, so I’m not sure how that would work. But I can say that water is able to get through into the casing of the grinder, so keep in mind when trying these things. As mentioned above, a blender is a better option if you have one.

If you are using more than a few drops that is already soaked into something else and likely won’t drip much, I’d highly advise against it (at least based on my experience).