Author here. Other experts in this field have also used the term "lambda reduction", including Levy himself [1] and Lamping [2], both which are referenced in the Delta-Nets paper. "Lambda-reduction" is clearly an abbreviation of Lambda-calculi reduction.

[1] https://dl.acm.org/doi/abs/10.1145/143165.143172

[2] https://dl.acm.org/doi/pdf/10.1145/96709.96711