Yep. Apple implied support would end around Sept. 2020, and considering virtually every previous update included an updated Safari, and the fact this one didn't, can only mean its the end to support.
Some food for thought for those concerned... don't be. Many Macs around the world are still running versions far older than High Sierra, and having no glaring security issues at all in 2020. Remember that Firefox still supports 10.9+, and Chrome still supports 10.10+.
Also, go check out the PowerPC forum. Everyone there is still using 10.5 or older online because of great open source projects like TenFourFox and Leopard Webkit. None of them have ever reported security issues, ever.