Just to kinda let you Understand.
Attack Speed affects 2 Things.
1.Attack Interval (-Infinity to 1000 ASPD) [Affects the Wait time before your Next Basic Attack]
2.Motion Speed (After 1000ASPD, Every 1000 ASPD gained = 1% Motion Speed) [Meaning at 2k/3k/4k/etc, Capped at 150%]
And that means.
Your "Attack Speed" is Maxed (0 second Attack Interval even with -2Billion Atk speed) But
Your "Motion speed" isn't maxed (Since ASPD Stats isnt Directly Modified)
Guess they need to change the Feature's Name to "Attack no Cooldown" or Something like that
but you get the point. [i hope]