Former rugby league star Williams appeared on the wing as a second-half sub to score two of his team’s 13 tries, having started at centre against Tonga last week.
“He made a statement, didn’t he?” Henry said, after seeing his team claim their second successive Pool A bonus point victory.
“When he went on he had a positive performance. He got the selectors thinking.”
Henry also highlighted the contributions of two-try wing Richard Kahui and flanker Jerome Kaino ahead of next Saturday’s pivotal group clash against France.
“We were better than last week. We played with better structure. The opposition wasn’t as good physically, but had good structure. We’ve been working on the breakdown. We wanted to get better than last week, and there were good signs of that.”
Skipper Keven Mealamu said: “We have improved a lot, but we still have a few things we can get better on.
“We have some talented boys who can play in different positions, and we’re building smoothly. But next week (v France) is a big step up.”
New Zealand shredded Japan at regular intervals with Kahui (2), Williams (2), Mealamu, centres Conrad Smith and Ma’a Nonu, full-back Isaia Toeava, scrum-half Andy Ellis, flankers Kaino and Adam Thomson, fly-half Colin Slade and Andrew Hore touching down.
Slade added nine conversions for a 23-point haul, although Japan at least gave their supporters something to cheer when wing Hirotoki Onozawa claimed a consolation score midway through the second half that Murray Williams converted.
NEW ZEALAND: Toeava, Jane, Smith, Nonu, Kahui, Slade, Ellis, Woodcock, Mealamu, O. Franks, Thorn, Whitelock, Kaino, Thomson, Vito.
Replacements: Weepu for Toeava (62), S. Williams for Jane (44), Cowan for Ellis (62), Hore for Mealamu (44), Afoa for O. Franks (64), Boric for Thorn (72), A. Williams for Vito (58).
JAPAN: Ueda, Usuzuki, Taira, Imamura, Onozawa, Williams, Hiwasa, Kawamata, Aoki, Fujita, Ono, T. Kitagawa, Taniguchi, Leitch, Kikutani.
Replacements: Webb for Ueda (52), Tupuailei for Taira (46), Yoshida for Imamura (71), Yuhara for Aoki (64), Hatakeyama for Fujita (60), Y. Kitagawa for T. Kitagawa (60), Vatuvei for Kikutani (60).
Referee: Nigel Owens (Wales).