Many Christians believe that Jesus abolished the Old Testament dietary laws. The dietary interpretation of Jesus' words (i.e. swine pig consumption) does not exist in the Textus Receptus Bible, the authoritative Greek New Testament text that was accepted by the Christian Church until about 100 years ago.
This parenthetic interpretation of Jesus words was obviously a comment that some Bible scribe wrote in the margin of the text. Later scribes accidentally or deliberately incorporated the marginal comment into the text itself, so the statement appears only in corrupted texts.
But the statement does not appear in the Textus Receptus, so the KJV says nothing about Jesus "declaring all foods clean."
God had clearly prohibited pig, swine and pork in the Old Testament. This verse was over whether or not 'unwashed hands' caused clean food to become unclean.
Because it entereth not into his heart, but into the belly, and goeth out into the draught, purging all meats?