PLO8 Surprising flop equity comparison

[otctrader]

Sorry I'm missing the full hand history, but here's the pokerhand equity comparison:

Flop - Kh 4c Tc

Cards:
4s Ad Ah 8h scoop-313 HIwin-356 LOwin-27 EV-.423
3s 5c 2c 4h scoop-440 HIwin-464 LOwin-179 EV-.577

Without getting too much into the context of the hand, I raised PF in EP with the AAxx, got heads up vs LAG button, potted flop, and was put all in by LAG holding the wheel cards.

When I ran the equity comparison, I was surprised to see how potent his hand was, considering there's only 1 low card on the flop - is his flush draw really that powerful?

If I were the LAG button playing against the EP raiser (and pegged EP on AAxx), I probably wouldn't put him all-in in this spot since I'd never guess I'm almost 60/40 with only one low card on the board. Am I missing something here?