In addition to spin-spin splitting or J-coupling, the chemical shift difference of two nuclei can offer a clue into the type of coupling present. For unsaturated sp2 carbons, diastereotopic geminal protons tend to exhibit a small chemical shift difference, less than 45 Hz, in comparison to that seen with vicinal protons. Please note that this guide offers significant variations and thus be used cautiously [1-2].
From the 1H-13C HMQC spectrum (Question and Solution), the two correlations are separated by 75 Hz. If the two nuclei are coupled, then it is less likely the correlations are a result of geminal hydrogen atoms (=CH2).
1. J. Heterocycl. Chem., 2005, v.42, p.293-296.
2. J. Magn. Reson., 1970, v.2, p.150.