I wouldn't say evil. Two-faced for sure, but it is a bit too soon to say whether she is actively malicious, or just after being the center of attention and popular by playing cutesy.
The difference is, like shinta said, in their relative knowledge level and their intentions. Banri realized he was being as just much of a dick as Linda is a liar by pretending he doesn't know his own family or old friends. Sure, they'd be hurt at first, and interact with him using kid-gloves, but eventually they'd get to know the current Banri if he allowed them to do so. He was pushing them away out of fear of hurting them.
Linda on the other hand, was actively deceiving him. What tips Banri off is those shoes. He knows Linda knows him at this point, and that they used to be quite close. He's amazed that a pair of shoes that a club member is trying to sell fit him perfectly. They're 20k Yen shoes! Then he finds out that Linda was trying to sell them. Moreover, once she finds out it's Banri who fits them, she gives them away for free. That wasn't a "impulse buy" and a sale, that was a very specifically chosen gift, but delivered in a very bizarre method. He's noticeably weirded out at each step in this process of that scene, but covers it up too at the end so the others don't notice.
Banri was unintentionally hurting others without realizing it, but he has no memories of them. They're strangers who tell him they're family. He thought by keeping them distant, that he was keeping them from being hurt by his not Tada Banri existence.
Linda has been clandestinely keeping Banri in her life, keeping him just within arm's reach, while very deliberately lying to his face.