Resistance training performed to volitional failure results in comparable muscle hypertrophy between low-load (20-25 repetitions) and high-load (3-5 repetitions) protocols in trained individuals.

Study: Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.

When people who already lift weights push themselves to their limit, it doesn’t matter if they use heavy weights for a few reps or light weights for many reps—both ways make their muscles grow about the same.

Study: Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis

The study found that lifting weights until you can't do more reps leads to similar muscle growth whether you use light weights for many reps or heavy weights for few reps, which matches the claim.

Study: Comparable Strength and Hypertrophic Adaptations to Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome

This study found that lifting light weights for many reps and heavy weights for few reps, both done until you can't lift anymore, made muscles grow about the same size in people who already work out.