You can't say the linesman was out of position, as he is supposed to be in line with the last defender to check for offside. Lampard took a shot from outside so he was where he was supposed to be, what you can say is the angle he was looking at it from, he probably couldn't be 100% certain if it crossed or not. So the question becomes should he have given it or not. His positioning was right though for what was happening at that time.
your point highlights how idiotic the current FIFA stance on goal mouth tech really is. How can a linesman be realistically expected to line up with the last defender for a free kick at the top of the box, then essentially travel as fast as the ball to reach the touch line to see if it fully crossed the line?
I don't care how fit your official crew is, they not making it. Replay tech easily catches these men out of position and huffing it, but by the time players spin round to protest they magically appear at the corner flag nodding yes or no with authority. It's a joke.
Back when I used to referee, I remember being in a workshop and a USSF assessor tell us, no matter what happen, once the free kick taken, find yourself at the corner flag. Like a magic show, it all about the slight of hand while the audience is distracted by the spectacle. Fortunately for them, magicians doh have to deal with instant replay.