Being at the Senior engineer level now, I find this resource a nice counterbalance against the abundance of existing material aimed at engineering management and the vast ocean of material for Junior engineers.
Really, it is only 2 different ways to contribute to a product and engage in a team. If you can be good at both, why force a career-long choice?
Tech leads are influencers, we focus a lot more on technology and growth of the team in a different way. You forgo all the messy (boring for me) details of project management, and focus more on the technology and getting the right people to move projects forward, but this requires persuasion. There's not one way to do this job, you have to find your own. The hardest part is probably that of picking the right thing to delegate, to maximize growth and project success.
There's some overlap with managers especially as you climb the ladder and your focus is more strategic than tactical.