Jones said: "It's disappointing with the lateness of the goal and the manner.
"We knew when they brought Matt Smith on what's going to happen and we've worked for that and we've had a big enough side.
"We've had two six-foot-plus players marking him on the back post and we still lose the header, so it's very disappointing the manner of their goal.
"The performance was positive, we made a lot of changes, it was chalk and cheese from the ineptitude that we showed on Saturday (against Stoke) so at least we had a reaction from them.
"When you've only got one you're always susceptible, especially against a side like these who go direct and we've come unstuck with that.
"I'm really disappointed, it's really hard to speak about all the positives as I feel so down and so disappointed for them, for us, because we probably deserved three points tonight.
"It's just one we've got to get the second goal and two we've got to defend that better."
A scrappy first half saw chances at a premium, Sluga saving at the feet of Tom Bradshaw and Ryan Tunnicliffe dragging wide.
Millwall boss Gary Rowett added: "It was just a lack of quality within our team today.
"I thought it was going to be a difficult game, we can't make lots and lots of changes, Luton made five, but we couldn't do that as we've got so many injuries.
"We started the game OK, I thought overall we had by far the better chances, but just couldn't play with that calmness in front of goal.
"It wasn't a great performance from us, but we did enough to get in some good positions and then our one moment of quality, Willo (Shaun Williams) looks like he's going to cross it, chops it back on to his right foot, puts over the cross, Smudge heads it and George continues a really good start to his Millwall career by getting us a point."