No it is not coincidence:
It is because units for mass, force and pressure have been choosen such that common ratios of those units (density of water $\rho_{Water}$, gravitational acceleration on earth $g$; pressure unit $1 at$) have values that are powers of 10. (Further improvements in measurement changed those values a little bit later on; especially $g$; that's why the values are not exactly $1.000\times 10^n$).
- 1 at is defined as the pressure of 10m water column
reference: "A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to one kilogram-force per square centimeter"
(The German Wikipedia article mentions the 10m water column; which is equivalent to weight of 1kg per cm²) - The density of water is not by coincidence (but by early definitions of unit of mass kg) almost exactly 1000kg/m³
- The gravitational acceleration $g$ is not by coincidence (but by early definitions of unit of force N) approximately 10N/kg (more exactly about 9.81N/kg; even more exact value depends on the place on earth (especially latitude)).
Putting that together you get:
roughly:
$1 at \approx 10 \times 1000kg/m³ \times 10N/kg = 100000 N/m² = 100000Pa$
more exact:
$1 at = 10 \times 1000kg/m³ \times 9.81N/kg = 98100 N/m² = 98100Pa$
or
$1 Pa = 1019 \times10^{-5}Pa$
EDIT:
I'm referring above to the value of 1 at (called "technical atmosphere") not the standard atmosphere.
Note that the title of the original question is ambiguous as it just mentions "1 atmosphere".