Draco's reaction, rather than increase Greg's apprehension, actually helped give him the courage to step forward. That was the Draco he remembered, especially in more recent times. It was something familiar, and Greg could handle familiar.
"Yeah, hi," he said, still feeling a bit awkward, as he stepped inside. "You told me I could come," he added apologetically. "If I'm disturbin', tho, I can go."