The message says 20.000x multiplier, so I assumed it was a 1 dollar bet that won 20k and that is why it is such a big achievement. Unless that guy played 20k+ times and lost, this is a great win for him because betting 1 dollar and getting 20k is a big deal. If someone wagered 200k and won 20k that wouldn't really be a tweet worthy thing, it wouldn't even be chat worthy thing, it would be something very normal and very expected overall, but it is a tweet worthy thing because his multiplier is huge.

Plus on slots games there are many times you win nothing, absolutely nothing but then something happens and suddenly you can have a huge win, that type of thing happens quite frequently on slots (not the frequency of how many times it happens back to back, but to how many people it happens) so I do believe that someone may have won that much on slots.