alph2z - From your point showing 1200' and 194 kts 4.5 n.m. to RWY 13 at LGA.
Airbus supposedly states you can glide 2.5-2.7 n.m. per thousand feet. Boeing gives about 3 n.m. per thousand.
Using that as an example you could go 3.6 n.m.'s, no wind, from the 1200'/194 kts position. Unfortunately the runway's 4.5 nm away.
It's interesting to see if they could have made it, but even if they'd started at the 2000'/202 kts position it's exactly 6 n.m. to RWY 13, which given the glide information provided would be the exact distance required to make the runway.
That's not considering wind or the loss in distance made good due to the 90 degrees of heading change needed to make LGA Rwy 13.
The manufacturer's gliding distances vs hight are probably correct but if I had a double flameout I'd use about 1.5 x hight at most to allow for the much steeper glide in landing configuration and also the need to aim to land deep, rather than in the usual area. At 1200ft AGL I wouldn't count on getting more than 2 miles.