Question about an interaction

Hello!

I was playing a game last night and one of the players was playing [[Zellix, Sanity Flayer]]

He had Zellix out and also [[Mindcrank]].

He claimed that each point of life lost counted as a separate mill instance so if I lost 5 life and milled 3 creatures he should be able to create a 1/1 token from Zellix's trigger for each creature milled, rather than just one.

I would have though losing 5 life would count as one instance of milling 5 cards, therefore only one token created.

The game was almost over at that point so I didn't bother arguing, but who is correct here?