This is normal. He probably is too excited by his new trick of walking, but it is also important to know that he is not growing as fast as he was 6 months ago so he does not actually need as much food. Most kids this age go through spurts--for a few days they eat everything in sight, and then for a few days they eat very little. Try to think about toddler nutrition in terms of what they eat in a week, not at one meal (or even in one day). Kids around this age notoriously get a bit more picky as well--this too is normal--it's a control thing, and he may do better with finger foods rather than purees. In any case, try not to worry too much. If he really doesn't seem to be eating much for a few weeks, bring him into the ped and make sure his weight is ok.
My sweet boy 8/06
My beautiful girl 10/09