There is a very specific metric that is used to distinguish whether a beam of light/EM wave is "classical" or "quantum". The metric is called the second order correlation function, labelled g^(2).
If a EM wave has g^(2)>1 then experiments that demonstrate quantum phenomena cannot be successfully performed with this wave. Hence, the EM wave is called classical. Only if g^(2) < 1 can you start doing quantum stuff with it.
In this case, almost certainly the waves have g^(2) > 1.
Coherence is a function of time/length though. At a sufficiently short time interval, all waves are coherent. It's effectively a measure of the time (or equivalently distance) between phase shifts.
Since they're claiming to use interference, which only exists in coherent waves, I think it's safe to say in g(2)<1 for the scale they're utilizing interference at. Coherence is so inexorably linked to interference, it's measured using an interferometer.
Simple water waves or simple sinusoidal EM wave (such as AM radio waves) display interference. Both are classical objects because their g^(2) > 1. You can look at, for instance, the g^(1) function to determine how nicely a particular wave interferes with itself.
Second order correlations directly test for the bosonic nature of photons. In quantum light, photons clump together because they are bosons, while in classical light photons are independent of each other and any clumping that happens is purely probabilistic. The g^(2) function tests this degree of clumping.
If a EM wave has g^(2)>1 then experiments that demonstrate quantum phenomena cannot be successfully performed with this wave. Hence, the EM wave is called classical. Only if g^(2) < 1 can you start doing quantum stuff with it.
In this case, almost certainly the waves have g^(2) > 1.