(Minor spoilers in this comment)
It's the first update in 2018... the year that's mentioned in Monika's character file...
Yes, I'm pretty sure it's Monika. There are a lot of youtubers who got this while doing a playthrough of the game, if it's paused at the right time it's shown that it's Monika by her orange hair and white bow. I think the words aren't different then ones shown before, regardless of what word you pick there's a set chance (I think 1/11 each time a word is clicked?) of Monika's chibi.
Did you have the game on auto? This is when the script just keeps going instead of you having to click it, the setting is in the text box. I had it on auto and it did the "uncaught exception" thing twice, but I was able to keep going. I think you just have to redownload it, maybe there was an actual glitch in the game (since it adds files and stuff like that while you're playing, it could have accidentally deleted one?) I don't know much about how these things work, but maybe check the game files to see if everything's there (except for the .chr files).
I'm replaying the game to get the good ending (I deleted it and reinstalled), but I just realized I also deleted the game files... the game seems to work normally without the game files, but if I get the Just Monika ending and have to delete her, I can't without the game files... does anyone know how to get the game files back? I know they're there, because the game is working normally, but they're not in my files anywhere.