What do limp hugs/huggers mean?

My ex came to me after a baby registry outing with the moms to give me a hug... it was so limp. walks away and says get a hold of me sometime... What does that mean? I mean of course it's awkward, we aren't dating anymore but we are pregnant together...but there has to be some psychological background, doesn't there?
What do limp hugs/huggers mean?
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