Guys take a look into this (I know, it's a 4 year comment, but people still having questions): https://resources.german.lsa.umich.edu/grammatik/nicht/
Duo isn't great when it comes to clear grammar rules.
Maybe the website has been edited since you posted this, but it clearly states now that "kein" is used to negate when the noun is not preceded by any article, as in "Gruppen". If the sentence said, "I do not like the groups", then it would be, "Ich mag die Gruppen nicht".
Yes, Mann can also mean husband. Usually you would have enough context to determine the appropriate translation. If there is no context I guess as a rule of thumb I'd suggest translating Mann with a possessive determiner to husband while a definite or indefinite article tends to be a man.
After listening to it several times in slo-mo, I consistently heard "koppen."
Listening to the forvo.com pronunciation, I hear "kruppen"
Thing is, I thought the German 'g' only changed from an English 'hard-g' to 'k' sound when at the end of a word (e.g., genug --> 'genuk', not 'kenuk')
Any guidance? Do I just need more ear-training?
while goup(s) is the more precise/accurate translation of gruppe(n)... with menschenmasse/etc. a direct translation for crowd... however, i feel like for just contextual, cultural norm usage consensus, its much more common to hear U.S. english speakers to say crowd to refer to the thought of multiple people, even small amounts (why we say 2's company, 3's a crowd). "groups" sounds weird especially since it connotes a type OF something, and it isnt implicit just to refer to people. it could be groups of whatever. so while crowd isnt a literal translation, figuratively it SHOULD be correct as a possibility (only the english version). it sounds weird here to end w/ the word group bceause theres almost always either a more specific word in english for types or sizes of group (gang, swarm, grabble, pack, band, herd, school, gaggle, mob, lot, flock, gathering, collection, assembly, entourage, clique, pair, CROWD) or it is followed with "---OF [insert type specifier]" 'he doesn't like groups' isnt flawed... it just isnt what i hear people here say.