I don't see any splitting on both NMR Spectra
If you noticed, the 3-methylbutanal NMR spectra was done under 400 MHz while the butanal was done under a 90 MHz spectra
the splitting you think you see on butanal NMR is because a 90 MHz display is not as fine as a 400 MHz display.
to confirn this, you need to have the splitting data
some sites allow you to zoom into each peak to determine it's splitting (singlet, doublet, multiplet...)
hope this answers your question