He meant to get revenge. He placed his company in an ambush site on the hill and waited until the British advance guard had turned the corner.
"About the middle of the forenoon Captain Parker having collected part of his company, I being with them, determined to meet the regulars on their retreat from Concord. We met the regulars in the bounds of Lincoln. We fired on them and continued so to do until they met their reinforcement in Lexington."
Nathan Munroe“Parker’s Revenge: Lexington’s Lost Battlefield,” National Park Service, 23 November 2021, https://www.nps.gov/mima/learn/historyculture/parker-s-revenge-lexington-s-lost-battlefield.htm.