Let's put it this way, I as an adult woman have had crushes on people that I haven't been dating and that I haven't been interested in. At no point would I say to them 'hey, I have feelings for you'.
Because that is not their burden to bare.
And because my feelings are not their responsibility.
You say it yourself, she has given him no reason to think she is into him. So why is it her responsibility to feel bad for not liking him? It isn't. But if he tells her he has 'feelings' for her, she then has to be the 'bad guy' saying no. He might be unburdened but she feels burdened. She knows she doesn't owe him anything (provided she has healthy self esteem)/but she still doesn't like hurting someone. Especially someone she has to continue to work with.
I worked with a guy once who I realised was getting the wrong idea. So I backed off. But wprking with him meant i couldnt avoid him. He must have asked me out about 4 times. Each time I politely made excuses. Eg: 'I'm too busy', eh...maybe we could invite others and make a group thing of it', not replying to texts changing subject. Trying not to be the bad guy but feeling worse and worse that he 'wasnt getting the message'. The truth is - he GOT the message. He knew I wasn't interested. That I was saying no. But he just wouldn't leave it. He was trying to guilt me into a date.
So I flat out told him I wasn't interested and enough was enough. He then begged me for a date. I said no. I ultimately left my job because it was so uncomfortable being around him.
Obviously I could have been like 'no' from the offset but i think as women, we are conditioned to to hurt men's feelings.
I am assuming your friend isn't as bad as my creeper. But if he if decent, he'll take a friggin hint. And if he really isn't sure she doesn't like him (which I doubt) he'll ask her out once and if she doesn't seem keen, back the feck off.