로 has many definitions and cases for usage. In this case, something changes "into" something else. A common similar case is foreign exchange, dollar change to Korean won. "원으로 바꾸다". The "from" and "to" you talk about is more likely "에서" "까지". Here is dictionary definition to show the many variations of 로 http://endic.naver.com/krenEntry.nhn?sLn=en&entryId=db967e4de5c24c5da9fdc793a262d075&query=%EB%A1%9C

My interpretation would be that you haven't yet reached the "endpoint" of fall yet, you are still transitioning from summer to fall, so thinking of -로 as "via" makes sense. Here in North Carolina, the season is changing from summer (through) to fall.