Time flows faster in the Quor'toth, and Holtz took at least a couple of Earth-hours to follow Connor through the rift. Holtz would have been alone in the Quor'toth for weeks, maybe even months, before following Connor's lead. When Holtz finds Connor, he acts like little to no time has passed at all, when in fact it might have been quite some time.
After the fight, Connor immediately returns to Holtz and Angel to Cordelia. Angel doesn't even comment on Connor's disappearance or reappearance.
When Angel finds Justine at the bar, he tells her to run, and she does. Why would she take advice from Angel? The reason she was at the bar in the first place was to fight vampires, so why not stay and fight them?
When the vampire that Connor is fighting escapes he follows it and then Angel follows him. In the overhead shot of them running out, a couple of vampires are visible laying on the ground and staggering to get up. It seems odd that Angel would leave those vampires there to hurt more people. He may not kill every demonic creature he comes across but since these vamps were actually attacking somone you'd think he would prefer them dead.
When Holtz finishes his voiceover, he says, "Lovingly, Your Father" but the closed captioning says, "Lovingly, Dad".
It is not explained how Justine was able to find Holtz at the motel.
Lorne: (Talking about Connor) That kid was toxic when he came in here tonight. Heavy on the "ick".
Angel: What actually happened out there?
Lorne: In my professional opinion? (indicates Cordelia) Well, Miss Demony-Britches here gave that child some kind of soul colonic. Flushed him out but good.
Holtz: I'm an old man now. I have nothing to offer the boy. You can give him what I can't - his purpose.
But every time you look upon his face, every time he calls you "father" you will be reminded of that which you took and can never give back. And if that is vengeance, I find I have no taste for it.
(Fred & Gunn spot Connor)
Fred: Looks like we've been following Angel's son's emissions this whole time.
Gunn: Now there's a sentence I don't ever need to hear again.
Fred: But that's good right? It means there was no big scary that came out of the portal.
(Fred & Gunn spot Holtz)
Gunn: How about a short scary?
Lilah: See you got my invitation.
Wesley: Lilah. Obviously.
Lilah: I thought the "come alone" was a particularly ironic touch. I mean, how else would you come?
Cordy: Wait! -Angel, before you go, we have to do that thing.
Angel: What thing?
Cordy: That thing we do? You know, that thing where I say 'Are you sure you know what you're doing?' 'Angel, please think about this' and then you ignore me and rush headlong into trouble?
Angel: Right, that thing. (pauses) ...'Kay, we done?
Lilah: (talking about Justine) She has been pissing off a lot of undead Americans lately.
Fred: (About Connor) Okay, so he survived an unspeakable hell dimension. Who hasn't?
Lilah: Who's the boy wonder?
The Boy Wonder was a nickname used for Batman's sidekick Robin in DC's Batman comic books. The creators of Angel have frequently mentioned elements of Angel that are intentionally Batman-like.