I saw in a episode of The Clone Wars, Yoda teaching younglings to build their lightsabers purely on force instinct. Does this explain how Luke was able to construct his own lightsaber?
No. In the novel "Shadows of the Empire", it explains that Luke built his second lightsaber (the one seen in Episode VI) using instructions & components he found in Ben Kenobi's hut. Luke lived in the hut for several months while planning the rescue of Han Solo from Jabba's palace.
Shadows of the Empire is no longer considered canon, so we will have to see if the new canon presented in Episodes VII-IX contradicts that.