chess slang?

Smurfing = a person intentionally playing on a lower-rated account
ELO = the ELO rating system; this refers to just rating in general
The person was accusing you of being much better than your rating and having an alternate "smurf" account to get easier wins.

Your opponent was just most likely salty (upset over a loss or a streak of losses to the point that they start making bad reactions like cursing at the opponent or downplaying their skill). But out of curiosity, can I take a look at those 3 games to see if the level of play seems balanced for both players or not?

I don't know how to attach games if that's possible.
First you go to the archive then select the game you want to share. Click the bottom left icon on the white box then copy the PGN shown. Go to the forums and you'll see a chess board icon on the top left of your posting board. Click it, then click Load from PGN and paste the PGN there.

My goodness... your opponent played incredibly poorly those first 2 games, even for an 800. No wonder they resorted to baseless accusations.