Wrong. If you actually pay attention to his arms and hands when she hugs him late in Chapter 4, you'll see that Cloud starts to reach up to hug her back but catches himself before he can slip out of his cool facade. He often tries to impress her, either with his cool merc talk and attitude or his fighting skills on the bike. She keeps flirting because she knows he doesn't really mean the harsh things he says. It's a front, and she knows it. He's a tsundere, and that means he's not used to warmth and affection like what she gives him and responds in the only way he knows how. And when she kisses him, he's surprised and startled, not uncaring. He's just so stunned he doesn't have any idea how to respond, so he doesn't. That doesn't mean he didn't like it. Also, watch his eye contact with her in the scenes they have together. His eyes follow her practically all the time. So much so that she has to move the materia she's holding in Sector 8 to get him to look at it and away from her.
He also never tells Jessie to stop holding onto him. In one of the bike end scenes, he actually tells her the opposite, to hold on tight. And when she hugged him outside her place, he could have easily pulled her off because of how strong he is as a SOLDIER. But the attempt he made was only half-hearted at best, which means he didn't mind it near as much as he let on. And not only could you choose to have him accept her invitation, the story treats it as the default choice because he mentions it to her later in the pillar, and before she does.
And he does warm to her by the end of Chapter 4. If you watch his face, you'll see he gives her a small smile just before he picks her up (watch how his mouth goes up slightly). And he didn't even have to carry her at all. If he really didn't care about her, he'd have let Barret carry her in or let her lean on Tifa. But he didn't do that. He got down and picked her up all on his own. Also, in the Japanese translation, he's much warmer and more tender to her as well. For instance, from the scene in the pillar:
English
Jessie: My hero... so gentle.
Cloud: Just try to hold on.
Japanese
Jessie: You saved me again...
Cloud: I'll save you as many times as you need.
Also, in Chapter 4 when she makes her invitation:
English
Cloud: Are you seriously that desperate?
Japanese
Cloud: Is this how it's gonna go?
And it was Jessie, not Tifa and not Aerith, that got Cloud to drop his hard edges. She's also the only one of them to have kissed Cloud on screen. Also, he encouraged her when she was down about being off the mission. Sure, that could just be a friend thing, but combine it with everything else and that becomes less certain. Also, how quick he was to agree to her request to cause havoc for her on the mission.