Seibu had nothing to do with it. BicCamera started in Ikebukuro and was influential in building up the area. The jingle change is a campaign as BicCamera is doing a cooperation with the ward to build it out more. See [1]
Sources:
Wikipedia – Sogo & Seibu: https://en.wikipedia.org/wiki/Sogo_%26_Seibu SBbit – Seibu Ikebukuro redevelopment: https://www.sbbit.jp/article/cont1/144891