When it's his entire history in the playoffs you can. Especially since he was playing really well heading into those playoffs.
While his playoff numbers over four games probably mean something, statistics are only as valuable as what they can be used to predict. Here are some things Hayward's playoff numbers mean less than:
1) His career numbers.
2) His numbers last season.
3) His agent's gut feeling on the numbers he'll put up next season.
4) His biggest fanboy on this forum pulling predictions out of his ***.
Odds are they mean more than the random integer I'm about to type, but I wouldn't put money on it:
3948713498719430170943810439810439817043913470
So, yes, you can use his playoff numbers to win some argument on this message board, but (if this was a smarter place) the credibility you lose by doing so would outweigh the near meaningless evidence you have.
Hayward's situation has changed so much that, personally, I wouldn't be confident in any model that tried to use past data to predict Hayward's next year (or his next playoff performance, whenever that is). Strange as it is, Hayward himself is probably the best judge in the world right now as to his own value, and even he might be way off.
I don't think it's worth the gamble to pay him a lot until we can gather more data about him in the role we'd be paying for.
I don't know what I'd do if I were Hayward. He could make millions betting on himself this year. Injury is the only real risk he'd be running, because someone will give him 10 mil per year, even if his efficiency drops off.