Since when was it off for women to use backpacks? It's a friggin' backpack!
It still is. See this excerpt from the OP's article for example:
Laura Wolf, who works at the Department of Health and Human Services in Washington, D.C., says several men have made jokes about whether she's off to a camping trip. "It's ridiculous to me because many men use full-sized backpacks that could actually hold camping gear," she wrote to me. Terese Souders told me she was asked by a co-worker if she was Dora the Explorer, patron saint of lady backpackers.