If it's an RC it will taste bitter, easy way to confirm and if you're experienced with psys you wont have consumed enough to ruin your day too much. Or else use a test kit/uv light. UV lights are good to confirm the presence of a chemical, by seeing the specs, but paper can glow too so the test kit is a much better choice.
As far as NBOMes/other chemicals being laid and sold as LSD since the NBOMe ban this has dramatically decreased, I haven't came across it since. Most RC blotters when laid these days will have the chemical name on the blotter, similar to 1p/al-lad/lsz, or a very unique blotter art. I would say your only going to encounter that risk if you live in the US or your at a festival. It doesn't make any sense for a decent dealer to put DOM on a blotter and sell it as LSD, you would never buy from them again.
Also if it was an NBOMe they definitely would have had strong colorful visuals. The alternative is a DOx and if it was that they would have been tripping for well over 12 hours.
Tldr: Ask your friend if it tasted bitter and get a test kit.