The benefits estimate on ssa.gov is based on your earning history up to this point and an estimate of how much you will earn until retirement.
Your estimate for age 62 assumes that you will work up until age 62. The age 70 estimate assumes you will work until age 70.
From the disclaimer on the estimate:
We estimated your benefit amounts using your average earnings over your working lifetime.
If you worked last year, we will also assume that you will continue to work and make about the same amount as you entered for last year's earnings (or the estimated annual future earnings you entered for your custom scenarios).
Generally, the older you are and the closer you are to retirement, the more accurate your retirement estimates will be. The estimates are more accurate when they are based on a longer work history with fewer uncertainties such as earnings fluctuations and future law changes.
It assumes that you will keep working after this year and that you will earn the same as you do now, up until you “retire” and start collecting benefits. However, you can customize the estimate by entering a future annual earnings amount. So if you just got a new job with a raise, you can enter that new number and see the benefits estimate rise. Conversely, you can enter a $0 amount there and find out what your benefits would be at retirement age if you stopped earning now.
“Retirement,” as far as Social Security is concerned, doesn’t necessarily mean that you have stopped working; it simply means that you have chosen to start collecting your Social Security benefits. There are limits to how much you can earn without reducing your benefits if you “retire” early, but if you start collecting benefits at “full retirement age” or later (age 67 if you were born after 1960), you can continue to earn as much or as little as you want while collecting Social Security benefits.