No it just means the button itself is registered not that it was pressed. It's a message that appears at boot in almost every x86 device. For example:
isab0: <PCI-ISA bridge> at device 17.0 on pci0 isa0: <ISA bus> on isab0 pcib5: <ACPI PCI-PCI bridge> at device 19.0 on pci0 pci4: <ACPI PCI bus> on pcib5 acpi_button0: <Sleep Button> on acpi0 acpi_button1: <Power Button> on acpi0 acpi_tz0: <Thermal Zone> on acpi0 acpi_tz1: <Thermal Zone> on acpi0 acpi_acad0: <AC Adapter> on acpi0You need to check the system logs for whatever the last thing shown was before it shutdown.
Steve